Control strategy for automatic shutdown of engine

ABSTRACT

A system is provided for automatically shutting down an engine of a portable or handheld device in response to the engine operating while in an enclosed space, such as a garage, shed, room, etc. to prevent dangers associated with carbon monoxide accumulating in the enclosed space. The engine has an oxygen sensor in its exhaust that is configured to detect the presence or absence of oxygen in the exhaust. Fuel can be removed from the air/fuel mixture (e.g., less fuel being injected) based on the output of the oxygen sensor to maintain a given desired air/fuel ratio. If the amount of fuel provided continues to decrease over time in order to maintain the air/fuel ratio, the controller can assume the engine is operating in confined spaces and can shut down the engine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.15/473,109 filed Mar. 29, 2017, the disclosure of which is herebyincorporated in its entirety by reference herein.

TECHNICAL FIELD

This disclosure generally relates to a control strategy forautomatically shutting down an engine. In particular, one or moresensors, such as an oxygen sensor in the exhaust and/or a temperaturesensor in the intake, outputs signals to a controller which, in turn,commands the engine to shut down based on certain characteristics ofthose signals.

BACKGROUND

Engines produce carbon monoxide (CO) gas, which is odorless, colorless,and toxic. Inhalation of carbon monoxide can be deadly. Gasoline-poweredgenerators include engines that produce carbon monoxide. If thegenerator is portable (i.e., can be easily picked up and carried by auser), the user might inadvertently be placed in an enclosed, partiallyenclosed, or poorly ventilated area in which the carbon monoxide cangather in concentrated amounts. As the engine of the generator continuesto operate while contained in the enclosed area, the concentratedamounts of carbon monoxide can become increasingly dangerous forindividuals.

Prior art engines may include a carbon monoxide (CO) sensor mounted onor around the engine or near the intake of the engine configured tomeasure CO content of the ambient environment and shut down the engineif CO exceeds a certain threshold. However, CO sensors can have inherentstability issues, are sensitive to humidity and temperature extremes,can lead to trailing off of signal quality, and are costly. While a COsensor directly measures the harmful gasses in the surrounding air, thequality and costs of the CO sensor can make this sensor undesirable incertain engine applications.

SUMMARY

According to one embodiment, a portable generator comprises an engine,an oxygen sensor, and a controller. The engine is configured to power anelectric energy source. The engine has an intake passage configured totransfer an intake, a combustion chamber, and an exhaust passageselectively coupled to the combustion chamber and configured to transferan exhaust after combustion within the combustion chamber. The oxygensensor is configured to output a signal indicating an oxygen content.The controller is coupled to the oxygen sensor and programmed to shutdown the engine based on the signal over time.

The oxygen sensor may be disposed in or adjacent to the exhaust passagesuch that the signal indicates oxygen content of the exhaust. The oxygensensor may be a switch-type sensor configured to detect a presence orabsence of oxygen in the exhaust.

The engine may further include a fuel injector for injecting fueldirectly or indirectly into the combustion chamber. The controller maybe programmed to command the fuel injector to inject an amount of fuelbased on the signal output by the oxygen sensor. The controller may beprogrammed to shut down the engine in response to the amount of fuelinjected decreasing over time. One or more additional sensors may beprovided and configured to output signals to the controller, wherein thecontroller is programmed to determine an air-to-fuel ratio based on thesignals from the one or more additional sensors, and wherein thecontroller is programmed to shut down the engine in response to theamount of fuel being injected decreasing over time while the air-to-fuelratio is maintained at a desired ratio.

The oxygen sensor may be disposed in or adjacent to the intake passagesuch that the signal indicates oxygen content of an atmosphere about thegenerator. The oxygen sensor may be a wideband oxygen sensor, and thecontroller may be programmed to shut down the engine in response to theoxygen sensor indicating a decreased amount of oxygen in the atmosphereover time.

They generator may not include a carbon monoxide sensor configured todetect an amount of carbon monoxide in the exhaust.

In one embodiment, a system for automatically shutting down an engine ofa portable devices is provided. The system includes an internalcombustion engine, and a power-generating unit coupled to the engine andconfigured to generate electric power from rotation of the engine. Afirst sensor is configured to output a first signal indicating an amountof power output from the power-generating unit. A second sensor isconfigured to output a second signal indicating a load placed on theengine. A controller is programmed to compare the first signal to thesecond signal, and shut down the engine in response to the load placedon the engine increasing over time while the rotational speed of theengine remains relatively constant.

The term relatively constant may mean remaining within a range of 5%deviancy.

The first sensor may be an engine-speed sensor and the first signal mayindicate a rotation speed of the engine which correlates to the poweroutput from the power-generating unit. The controller may be programmedto shut down the engine in response to the load placed on the engineincreasing over time while the power output from the power-generatingunit remains relatively constant.

The first signal may indicate watts, voltage, and/or amperage output bythe power-generating unit.

The engine may include a throttle plate configured to alter an amount ofair into a combustion chamber of the engine. The second sensor may be athrottle positions sensor and the second signal may indicate a positionof the throttle plate. The controller may be programmed to shut down theengine in response to the position of the throttle plate increasing overtime while the rotational speed of the engine remains relativelyconstant.

The second sensor may be an air pressor sensor located on or adjacent anintake of the engine. The second signal may indicate a pressure of anair intake.

The controller may be programmed to command the shutdown of the engineonly after an initial, controllably fixed delay after the engine hasstarted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a four-stroke engine with fuel injection andvarious sensors coupled to a controller programmed to perform actionsdescribed herein, according to one embodiment.

FIGS. 2A-2B is a schematic of a two-stroke engine with various sensorscoupled to a controller programmed to perform actions described herein,according to one embodiment, in which FIG. 2A illustrates the engine inan induction and compression phase, and FIG. 2B illustrates the enginein an ignition and exhaust phase.

FIG. 3 is a graphical representation of a comparison of engine speed,oxygen content in the intake or surroundings, an intake temperature, anda carbon monoxide content in the intake or surroundings, when the engineis operating in a confined space or enclosure, according to oneembodiment.

FIG. 4 is a flow chart representing an algorithm performed by thecontroller according to one embodiment to automatically shut down theengine.

FIG. 5 is a flow chart representing an algorithm performed by thecontroller according to another embodiment to automatically shut downthe engine.

FIG. 6 is a flow chart representing an algorithm performed by thecontroller according to another embodiment to automatically shut downthe engine.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments can take various and alternative forms. Thefigures are not necessarily to scale; some features could be exaggeratedor minimized to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the embodiments. Asthose of ordinary skill in the art will understand, various featuresillustrated and described with reference to any one of the figures canbe combined with features illustrated in one or more other figures toproduce embodiments that are not explicitly illustrated or described.The combinations of features illustrated provide representativeembodiments for typical applications. Various combinations andmodifications of the features consistent with the teachings of thisdisclosure, however, could be desired for particular applications orimplementations.

FIG. 1 shows one embodiment of an internal combustion engine 10. Theengine 10 may be configured and sized for small-engine applications suchas a portable generator, lawn and garden tools (e.g., weed trimmers,blowers, water pumps, snow blowers, hand-held equipment, etc.) and thelike. The illustrated engine 10 is but one embodiment of a four-strokeengine in which the engine operates on a four-stroke combustion cycle.The engine includes a cylinder block 20, which defines a cylinder bore22. A piston 24 reciprocates in the cylinder bore 22. A cylinder headassembly 26 is affixed to one end of the cylinder block 20 and defines asingle combustion chamber 34 with the piston 24 and cylinder bore 22.Both ends of the cylinder block 20 are closed with a crankcase member(not shown) defining a crankcase chamber 25 therein.

The engine includes an air induction system 14 and an exhaust system 16.The air induction system 14 is configured to supply air charges to thecombustion chamber 34. An air intake passage 40 is opened and closed byan intake valve 44. When the intake passage 40 is opened, air form theintake passage (e.g., the pipe or passage extending to the left of theintake passage 40) flows into the combustion chamber 34.

A throttle body may also be provided with a throttle plate 60 forpivotal movement about an axis 66 of a throttle shaft 68, which extendsgenerally vertically through the throttle body. A throttle positionsensor 62 may be provided approximate the throttle shaft 68. A signalfrom the throttle position sensor 62 is sent to an engine control unit(ECU) or controller 80 via a throttle position data line 76 for use incontrolling various aspects of engine operation include, for example,fuel injection control and ignition timing. Such control is described inU.S. Pat. No. 7,225,793 (“the '793 Patent”), which is herebyincorporated by reference in its entirety. As will be described below, a“load” signal (data indicating the load acting on the engine) may bedetermined not directly from the throttle position sensor but from anair pressure sensor 64. The load signal may be obtained through signalprocessing of the intake air pressure fluctuations as provided by theair pressure sensor 64.

In operation, air is introduced into the powerhead 12 and passes throughthe inlet opening of the plenum chamber. During operation of the engine10, an air charge amount is controlled by the throttle plate 60 to meetrequirements of the engine 10. The air charge then flows through therunner into the intake passage 40. As described above, the intake valve44 may be provided at the intake passage 40. When the intake valve 44 isopened, the air is supplied to the combustion chamber 34 as an aircharge. Under idle running condition, the throttle plate 60 may begenerally closed. The air, therefore, may enter the intake passage 40through the idle air adjusting unit (not shown) which is controlled bythe controller 80. The idle air charge adjusted in the adjusting unit isthen supplied to the combustion chamber 34 via the intake passage 40.The speed (rpm) of the engine 10 at idle may be adjusted by varying thesmall opening in the throttle plate 60. This is accomplished byadjusting a set screw (not shown) to limit the lower travel of thethrottle plate 60 about axis 66.

The exhaust system 16 is configured to discharge burnt gases, or exhaustgases, from the engine's 10 combustion chamber 34. The exhaust port 86is defined by the cylinder head assembly 26 and is opened and closed bythe exhaust valve 46. When the exhaust port 86 is opened, the combustionchamber 34 communicates with an exhaust pipe or exhaust passage 88,which guides the exhaust gases downstream through the exhaust system 12.

One or more camshafts (not shown) may be provided to control the openingand closing of the intake valve 44 and the exhaust valve 46. Thecamshaft may have cam lobes that act against valves 44, 46 atpredetermined timing in relation to the crankshaft 30 to open and closethe intake passage 40 and exhaust port 86. The camshaft is journaled inthe cylinder head assembly 26 and may be driven by a chain or belt (notshown) mechanically connected to the crankshaft 30.

The engine 10 also includes a fuel injection system 15. The fuelinjection system 15 may include a fuel injector 67 which has aninjection nozzle exposed to the intake passage 40 or intake passage sothat fuel is directed toward the combustion chamber 34. The fuelinjector may be provided in other locations, such as directly adjacentto the combustion chamber or in the crank case. The fuel injector maytherefore inject fuel either directly or indirectly to the combustionchamber. A main fuel supply is located in a fuel tank (not shown) fromwhich fuel is supplied via fuel system (not shown). Fuel is dawn fromthe fuel tank through a fuel filter (not shown) by a fuel pump (notshown). The pressure of the fuel is regulated by a fuel pressureregulator (not shown) and the fuel is sent to the fuel rail (not shown)and provided to the injector 67 for injection into the combustionchamber 34. Excess fuel that is not used by the injectors is fed througha fuel return line that is provided back to the fuel tank. The timingand duration of the fuel injection pulse may be dictated by thecontroller 80, as described in the '793 Patent.

The fuel charge from the fuel injector 67 enters the combustion chamber34 with an air charge at the moment the intake valve 44 is opened. Sincethe fuel pressure is regulated by the pressure regulator, a durationduring which the nozzles of the injector 67 are opened is determined bythe controller 80 to measure the amount of fuel to be injected by thefuel injector 67. The controller 80 through the fuel injector controlline 72 thus controls the duration and the injection timing in order todispense a mass of fuel. Preferably, the fuel injector 67 has nozzlesthat are opened by solenoid action, as is known in the art. Thus thefuel injector control line 72 signals the solenoids to open and closeaccording to the timing and duration determined by the controller 80.

The engine 10 further includes an ignition system, generally indicatedby reference to numeral 67. A spark plug 65 is fixed to the cylinderhead assembly 26 and is exposed to the combustion chamber 34. The sparkplug 65 ignites the air and fuel charge mixture in the combustionchamber 34 with timing as determined by the controller 80. For thispurpose, the ignition system 69 may include an ignition coil (not shown)interposed between the spark plug 65 and the spark plug control line 70.

The engine 10 also may have an AC generator (not shown) for generatingelectrical power. Additionally, the engine 10 may have a battery orother energy storage medium (not shown) for storing electrical energyfrom the AC generator and to supply power to the controller 80, theengine sensors (intake air temperature sensor 63, throttle positionsensor 62, intake air pressure sensor 64, crankshaft position sensor65), fuel pump, fuel injector 67, and the ignition coil.

A crank position sensor 65 may be provided to measure the crank angleand send it to the controller 80. In the illustrated embodiment, thecrank position sensor 65 is in the form of a crank trigger, which isconfigured to emit a single pulse (e.g., in an electronic fuel injectionengine) or multiple pulses (e.g., in a capacitor discharge ignitionengine) for each revolution of the crankshaft 30. Optionally, the cranktrigger can be configured to emit evenly-spaced pulses with a missingtooth as is known in the art. The signal from the crank position sensor65 is transmitted to the controller 80 via a crank position data line79.

Engine load can be sensed by the angle of the throttle plate 60, and issensed by the throttle position sensor 62 and is transmitted to thecontroller 80 via the throttle position data line 76. Engine load canoptionally be measured as described in the '793 Patent.

An intake air temperature sensor 63 measures the temperature of theincoming air in the intake (e.g., upstream of the throttle). The signalfrom the intake air temperature sensor 63 is transmitted to thecontroller 80 via the intake air temperature data line 78.

The intake air pressure sensor 64 is connected to the intake runnerbetween the throttle plate 60 and the intake passage 40 and measures thepressure of the incoming air charge in the induction air passage. Themeasurement of the intake air pressure sensor 64 is transmitted via theintake air pressure data line 74 to the controller 80. The intake airpressure data from the sensor 64 can be processed according to thedisclosure of the '793 Patent, for example, to obtain engine operationaldata in addition to pressure. In one embodiment, a minimum intake airpressure can be used to calculate an incoming air mass on acylinder-by-cylinder basis. Signal processing of the analog signal ofthe intake pressure also allows the system to determine engine phase,load, approximate position, and speed of the engine.

The controller 80 computes and processes the detected signal from eachsensor based on a stored control map. The controller 80 forwards controlsignals to the fuel injector 67 and spark plug 65. Respective controllines 70, 72 are indicated schematically in FIG. 1, which carry thecontrol signals.

While not shown herein, an oxygen (02) content sensor may be providedon, in, or adjacent to the exhaust passage 88. This type of sensor is,however, illustrated in FIGS. 2A-2B described below. The oxygen sensoris configured to detect the content of oxygen in the exhaust gas andtransmit a signal representing such content to the controller 80.

The embodiment described with reference to FIG. 1 is but one embodimentof a four-stroke engine. FIGS. 2A-2B below describe a two-stroke enginethat may utilize the teachings of the present disclosure.

FIGS. 2A and 2B show one example of an internal combustion engine 210.The engine 210 may be configured and sized for small-engine applicationssuch as a portable generator, lawn and garden tools (e.g., weedtrimmers, blowers, water pumps, snow blowers, hand-held equipment, etc.)and the like. The engine shown in FIGS. 2A and 2B is a two-stroke enginein which two different phases are shown that one of skill in the artwould recognize as an induction and compression phase (FIG. 2A) and anignition and exhaust phase (FIG. 2B), as will be described below.

The engine 210 includes a cylinder block 212 which defines a cylinderbore 214. A piston 216 reciprocates in the cylinder bore 212. Movementof the piston 216 turns a crankshaft 218 via a connecting rod 220 thatturns within a crank case 222.

It should be noted that the engine of this disclosure is not limited tothat shown in FIG. 2A-2B; the engine may include more than one cylinder,and may be of other types (V-type, Inline, W-type, etc.). Also, whilethe engine shown in FIGS. 2A-2B is a two-stroke engine, whereappropriate the engine may also be a four-stroke engine such as thatdescribed above.

The engine 210 includes an inlet port or intake passage 226 configuredto transfer an air/fuel mixture from a manifold into a cavity of theengine, such as the crank case 222. When the side wall of the piston isabove the end or opening of the intake passage 226, as shown in FIG. 2A,the intake passage is open and the air/fuel mixture can enter the crankcase 222. When the side wall of the piston covers the end or opening ofthe intake passage 226, as shown in FIG. 2B, the intake passage isclosed and the air/fuel mixture is prevented from entering the crankcase 222. The combination of the piston and the intake passage thereforeoperates as a valve to selectively allow the air/fuel mixture to enterthe crank case 222. In other embodiments, a reed valve may also bepresent in the intake passage to selectively allow the air/fuel mixtureinto the crank case 222.

A transfer port 228 fluidly couples the crank case 222 to a combustionchamber 230 that is defined within the cylinder bore above the head ofthe piston 216. The sidewall of the piston 216 covers the transfer port228 in FIG. 2A such that the air/fuel mixture is prevented from enteringthe combustion chamber at the end of compression and the moment ofignition and combustion. The engine may include a spark plug 232 toignite the compressed air/fuel mixture by an electric spark during theignition phase.

The engine 210 is also provided with an exhaust passage 234 that isconfigured to transport the resultant gases from combustion out of thecombustion chamber 230. During the ignition and exhaust phase shown inFIG. 2B, the piston has moved down so that the sidewall of the pistoncovers the intake passage or intake passage 226, but has opened theexhaust passage 234. When the piston travels down far enough, the pistonalso opens the exit of the transfer port 228 to allow the air/fuelmixture to enter the combustion chamber 230.

The intake passage 226 may be provided with a throttle assembly orthrottle body such as that disclosed in the '793 Patent. The throttle240 may include a throttle plate that pivots about an axis and isoperated by a throttle cable. Opening the throttle plate at variousangles controls the amount of air/fuel mixture entering the crank case222. A throttle position sensor 242 may be provided in or adjacent tothe intake port or intake passage to send a signal to a controller(described below) relating to the position of the throttle plate,indicating an amount of air/fuel mixture intended or commanded to enterthe crank case 222.

The engine and surrounding structure is provided with various sensors.These sensors are electrically connected to send signals to an ECU orcontroller 250, explained in more detail below. For example, an intakeair temperature sensor 242 may be provided in or adjacent to the intakepassage for sensing the temperature of the air (or air/fuel mixture) inthe intake passage 226 and relaying such data to the controller. Theintake air temperature sensor 242 may be provided upstream of thethrottle 240, but alternatively or additionally an intake airtemperature sensor may be provided downstream of the throttle within inthe intake passage 226. An intake air pressure sensor 246 may beprovided in or adjacent to the intake passage for sensing the pressureof the air (or air/fuel mixture) in the intake passage 226 and relayingsuch data to the controller. The intake air pressure sensor 46 may beprovided downstream of the throttle 240, but alternatively oradditionally an intake air pressure sensor may be provided upstream ofthe throttle within the intake passage 226.

An oxygen (e.g., O₂) sensor 248 may be provided in or adjacent to theexhaust passage 234 for sensing the oxygen content of the exhaust. Inone embodiment, the sensor 248 is a switch-type sensor configured todetermine the presence or absence of oxygen in the exhaust. In anotherembodiment, the sensor 248 is configured to detect the percentage ofoxygen in the exhaust. In either embodiment, the oxygen sensor 248 maybe considered to detect an oxygen content in the exhaust. If provided atthe exhaust passage 234 rather than the intake passage 226, the oxygensensor need not be a wideband oxygen sensor, which may be expensive.However, in some embodiments, a wideband oxygen sensor may be providedon the intake passage 226 to determine the oxygen content of the intake(e.g., fresh air).

The sensors explained above are exemplary and it should be understoodthat more or less of the sensors may be provided to provide data to thecontroller 250. While illustrated as a single controller 250, thecontroller may in fact be part of a larger control system and may becontrolled by various other controllers throughout the engine andsurrounding structure. Because all of these controllers can becommunicatively coupled to one another to issue various commands aboutthe structure (e.g., generator), the word “controller” in the generalsense is intended to mean one or more controllers communicativelycoupled to one another. This is also true with the controller of FIG. 1.

Furthermore, the controller may be or include a processor ormicroprocessor or central processing unit (CPU) in communication withvarious types of computer readable storage devices or media andprogrammed to perform various actions described herein based on thereceived signals from the sensors. Computer readable storage devices ormedia may include volatile and nonvolatile storage in read-only memory(ROM), random-access memory (RAM), and keep-alive memory (KAM), forexample. KAM is a persistent or non-volatile memory that may be used tostore various operating variables while the CPU is powered down.Computer-readable storage devices or media may be implemented using anyof a number of known memory devices such as PROMs (programmableread-only memory), EPROMs (electrically PROM), EEPROMs (electricallyerasable PROM), flash memory, or any other electric, magnetic, optical,or combination memory devices capable of storing data, some of whichrepresent executable instructions, used by the controller in controllingthe engine.

The controller may communicate with various engine sensors and actuators(such as those described above) via an input/output (I/O) interface thatmay be implemented as a single integrated interface that providesvarious raw data or signal conditioning, processing, and/or conversion,short-circuit protection, and the like. Alternatively, one or morededicated hardware or firmware chips may be used to condition andprocess particular signals before being supplied to the CPU. Asgenerally illustrated in the representative embodiment of FIGS. 1-2B,the controller may communicate signals to and/or from the varioussensors described above, as well as other sensors, and other associatedstructure such as a fuel injector, fuel igniting source, etc. Althoughnot explicitly illustrated, those of ordinary skill in the art willrecognize various functions or components that may be controlled bycontroller within at least each of the structures or subsystemsidentified above. Representative examples of parameters, systems, and/orcomponents that may be directly or indirectly actuated using controllogic executed by the controller include fuel injection timing, rate,and duration, throttle valve position, spark plug ignition timing (forspark-ignition engines), intake/exhaust valve timing and duration, andthe like. Sensors communicating input through the I/O interface may beused to indicate crankshaft position, engine rotational speed, intakemanifold pressure (MAP), ignition switch position, throttle valveposition, intake manifold air temperature, exhaust gas oxygen content,or other exhaust gas component concentration or presence, or intake airflow (MAF), for example.

Control logic or functions performed by controller may be represented byflow charts or similar diagrams in one or more figures. These figuresprovide representative control strategies and/or logic that may beimplemented using one or more processing strategies such asevent-driven, interrupt-driven, multi-tasking, multi-threading, and thelike. As such, various steps or functions illustrated may be performedin the sequence illustrated, in parallel, or in some cases omitted.Although not always explicitly illustrated, one of ordinary skill in theart will recognize that one or more of the illustrated steps orfunctions may be repeatedly performed depending upon the particularprocessing strategy being used. Similarly, the order of processing isnot necessarily required to achieve the features and advantagesdescribed herein, but is provided for ease of illustration anddescription. The control logic may be implemented primarily in softwareexecuted by a microprocessor-based engine controller, such ascontroller. Of course, the control logic may be implemented in software,hardware, or a combination of software and hardware in one or morecontrollers depending upon the particular application. When implementedin software, the control logic may be provided in one or morecomputer-readable storage devices or media having stored datarepresenting code or instructions executed by a computer to control thevehicle or its subsystems. The computer-readable storage devices ormedia may include one or more of a number of known physical deviceswhich utilize electric, magnetic, and/or optical storage to keepexecutable instructions and associated calibration information,operating variables, and the like.

Engines, such as the engines 10 and 210, consume oxygen available in thecombustion chamber and produce carbon monoxide (CO) gas as a byproductof combustion. Inhalation of carbon monoxide can be deadly. If theengine is part of a portable device such as a generator, lawn equipment,etc., a user might inadvertently place the portable device with itsengine running in an enclosed, partially enclosed, or poorly ventilatedarea where the carbon monoxide can gather in concentrated amounts. Asthe engine of the generator continues to operate while contained in theenclosed area, the concentrated amounts of carbon monoxide can becomeincreasingly dangerous for individuals. Carbon monoxide sensors can beused to detect an increase in CO and shut down an engine, but have theirinherent deficiencies, including accuracy and cost.

Therefore, according to various embodiments of this disclosure, a systemfor determining that the engine is running in an enclosed space isprovided. In various embodiments, a CO sensor is not provided. Instead,other sensors (such as those illustrated in FIGS. 1 and 2A-2B) providedata that allow the controller to infer that oxygen is being reducedfrom ambient air, or that the engine is in a confined space whereconcentrated carbon monoxide may become hazardous. And, the controllercan estimate the size of the enclosed space based on, for example, adetermination of the oxygen content of the exhaust and/or thetemperature of the intake. These and additional embodiments are providedbelow.

With reference to FIGS. 3-6 described, below, references to thecontroller and various sensors are made. It should be understood thatthese references can refer to the controller and various sensors ofeither FIG. 1 (in the case of a four-stroke engine) or FIGS. 2A-2B (inthe case of a two-stroke engine).

Before explaining various embodiments of algorithms employed by thecontroller, a comparison of data received by the controller isillustrated in FIG. 3. FIG. 3 shows a comparison of engine speed (RPM),oxygen content in the intake (e.g., surrounding environment),temperature of the intake, and carbon monoxide content. The engine of agenerator producing the data shown in FIG. 3 is placed in a confinedspace in which carbon monoxide can potentially accumulate to a hazardouslevel. While the engine itself may not include a CO sensor or an oxygensensor at the intake (as explained above), the content of the CO in theair is shown in the graph for comparative purposes. The data shown inthe graph is shown over time until the engine naturally stalls, withoutimplementation of the various control strategies described herein forautomatically shutting down the engine prior to it naturally stalling.

At approximately t=0, the engine is started. The speed of the engine(RPM) is determined from a crankshaft position sensor, or from airpressure as explained in the '793 Patent. The controller also receivesinformation regarding the oxygen content of the exhaust (and, in someembodiments, the intake), provided by the oxygen sensors. The controlleralso receives information regarding the temperature of the intake airfrom the intake air temperature sensor. While not illustrated herein,the controller may also receive data indicating other information suchas the throttle angle from the throttle position sensor, generator power(e.g., watts, volts, amps) output from the generator, engine load, airpressure received from the intake air pressure sensor, air mass, airvolume or flow rate from an associated sensor, etc.

Once the engine is started, the oxygen content of the intake is shown tobegin decreasing. At approximately t=120 s, a noticeable decrease inengine speed is illustrated, indicating load being applied to thegenerator and the door or opening of the room being shut to furtherenclose the engine in its surrounding environment. The rate of decreaseof the oxygen may be generally linear for a given engine speed and load;a reduction in ambient oxygen levels can indicate the engine is in aconfined space. As the engine consumes the oxygen through combustion ina finite volume of air, the amount of oxygen by volume is reduced.Likewise, the temperature of the intake is increasing. This can lead thecontroller to infer that the engine is operating in a confined spacewhere ventilation is not provided. Should an engine be run in free airand not in a confined space, the air acts as a near-infinite heat sinkand air temperature does not increase beyond a certain threshold.

Utilizing the data indicating the negative rate of change of the oxygencontent, the controller can determine a size (e.g., volume) of theenclosure surrounding the engine and can shut down the engineaccordingly. Temperature changes can be utilized as confirmation of theshutdown, in some embodiments. For example, if the controller determinesthat the oxygen content is decreasing at a rate of 1% per 100 seconds,and the intake temperature is increasing at a rate of 1 degree Celsiusper 100 seconds, the controller may determine that the enclosed spacearound the engine is approximately 500 cubic feet. In another example,if the controller determines that the oxygen content is decreasing at arate of 0.5% per 100 seconds, and the intake temperature is increasingat a rate of 0.5 degrees Celsius per 100 seconds, the controller maydetermine that the enclosed space is approximately 2000 cubic feet. Thecontroller may communicate with a stored lookup table in the associatedmemory that provides a volume that corresponds to a rate of change ofboth the oxygen content and the temperature from previous testings.

In other embodiments, the temperature alone can indicate the estimatedsize of the enclosure. For example, tests can be run and a lookup tablecan be created that correlates a rate of temperature increase to acorresponding size of the enclosure. The overall concept provided by thelookup table is that slower the temperature increases, the larger theenclosure is.

In other embodiments that will be described below, the oxygen contentalone can indicate the estimated size of the enclosure. Again, tests canbe run and a lookup table can be created that correlates a rate ofoxygen depletion to a corresponding size of the enclosure. The overallconcept provided by the lookup table is that the faster the oxygendepletion, the smaller the enclosure.

The estimation of room size of volume of the confined space may be animportant factor in determining how quickly the controller shuts off theengine. For example, if the controller determines that the confinedspace is small and the threat of CO exposure is significant, thecontroller may be programmed to be more sensitive by reacting faster orincreasing the frequency of sampling the environment. Conversely, if thesystem determines that the room is large or open to the free air, thesystem may make less periodic measurements or generally be lesssensitive to shutting down.

In one embodiment, the size of the enclosure or room can be estimatedwith the oxygen sensor alone without utilizing data from the airtemperature sensor, as explained in more detail below.

At approximately t=475 s, the engine speed begins to oscillate abruptlydue to the decreased amount of oxygen in the air, yielding undesirablecombustion characteristics. At this point, the oxygen content availablein the room does not support the combustion torque required to maintainpower generation. The engine then stalls at about t=520 s due to theoxygen content dropping to an unworkable level. For example, ambient airmight have a normal oxygen content of 21%; however, when the oxygencontent reaches approximately 17-18%, this might force the engine tostall, depending on the characteristics of the engine and load applied.

While the above embodiment takes roughly 520 seconds for the engine tostall, the carbon monoxide content in the air might already be lethal.For example, a level of 400 parts per million (PPM) of CO content in theair may be lethal with enough exposure. This amount is reached wellbefore the 520 seconds that it takes for the engine to stall. Therefore,it is particularly desirable to be able to shutdown the engine as earlyas possible, once the controller determines with accuracy that theengine is running in a confined space. Based on the rates of changes ofboth the oxygen content in the exhaust and the temperature of theintake, the controller may be programmed to automatically shutdown theengine to prevent the carbon monoxide from reaching dangerous levels.

FIG. 4 illustrates an algorithm 400 according to one embodiment that canbe implemented by the controller. In this embodiment, the controller canautomatically shut down the engine based on the oxygen content of theexhaust alone. At 402, the controller determines that the engine is onand running. This can be determined by, for example, the engine speedsensor as described herein. If the engine is not on, the control canexit the algorithm. At 404, the controller determines the oxygen contentin the exhaust, according to the methods described above.

At 406, the controller compares the magnitude or absolute value of therate of change of the oxygen

$( {\frac{{dO}_{2}}{dt}} )$

to a corresponding oxygen rate of change threshold. If the oxygencontent of the exhaust is changing at a rate that exceeds a threshold,then the controller commands the engine to shut down at 408. In oneexample, the threshold is 1% per 100 s. However, the threshold can varybased on the determined size of the room, which may be influenced by therate of decrease or amount of the oxygen and the rate of increase of thetemperature of the intake.

If the oxygen sensor is a switch-based sensor (as described in moredetail herein), the rate of change of the oxygen content of the exhaustcan be determined by the amount of time that the switch takes to switch.For example, if the calculated fuel mass is too large, the system willtake longer to switch lean. If the calculated fuel mass is too little,it will take longer to switch rich. The change in oxygen content in theair can therefore be indicated by monitoring the amount of negative O₂correction over time, as explained below. This indicates that oxygencontent is being consumed from the local environment and the engine isoperating in a confined space.

The use of the oxygen measurements explained above may be delayed untilafter startup of the engine. During an engine startup, an increasedamount is used to assist in starting and warming of the engine. Theoxygen measurements and associated algorithm described herein may not befunctional during startup, as implementation of the algorithm may haltthe starting process while the engine is trying to drive towards astoichiometric ratio. During the engine start, the controller performs acheck of the sensors to ensure that the sensors are working properly.This can include a test for sensor presence, an output of rationalvalues from the sensors, and no errors when codes are set in readingdata from the sensors. This can be considered a “calibration” exerciseevery time the engine is started. Accurate data may either be difficultto obtain during the startup, and therefore the engine-shutdownalgorithms described herein may be delayed until after the calibrationexercise or until after a certain fixed time threshold (e.g., 90seconds) after starting the engine. Once the engine is warm and thesensors are considered in good working condition, the controller canbegin sampling the data from the various sensors for the engine-shutdownanalysis described herein. The controller compares the sample toperiodic measurements of engine operation over time to determine if andwhen to shut down the engine. The system may periodically obtain newsample data to compare with the current running data of the engine.

The algorithm of FIG. 4 is but one embodiment. Estimation of the size ofthe room or enclosure can be performed with the oxygen sensor alone;other data such as a rising temperature may serve as support for theinference that the engine is operating in a confined space. Duringcombustion in a four-cycle engine at stoichiometry, all oxygen in thecombustion gases is consumed. The oxygen sensor on the exhaust may be ofa switch type or wideband. A closed-loop control may be implemented bycontrolling the air/fuel mixture just slightly rich/lean or stoic andwatching the oxygen sensor switch. This may be referred to as a“bang-bang” since a switch type sensor (if utilized on the exhaust) onlysenses a presence or absence of oxygen in the exhaust. If oxygen ispresent, the engine is running lean; if no oxygen is present, the engineis running rich. Effectively, the control loop verifies that the airmass (and matching fuel mass) is correct. If the calculated fuel mass istoo large, the system will take longer to switch lean. If fuel is toolittle, it would take longer to switch rich. Meanwhile, the controlleris incrementally changing the air/fuel ratio up and down (e.g., byadjusting fuel injection opening duration) by small amounts and lookingfor the oxygen sensor in the exhaust to switch. The small incrementalchange in the air/fuel ratio are to attempt to maintain combustion at ornear the stoichiometric ratio.

A closed-loop system may be provided in which the sensors and associatedcontrol measure the air mass, and then alter the amount of fuel added tothe air to maintain the desired air/fuel ratio. Then, data from theoxygen sensor will be analyzed to determine the effect of removing thefuel. The air/fuel ratio will be compared to the desired air/fuel ratio.For example, if a stoichiometric ratio (λ=1.0) is desired, and thecurrent ratio is λ=1.05, the controller may alter the amount of fuelaccordingly in an attempt to return the ratio to λ=1.0.

Negative O₂ correction can be realized when the controller is commandingmore and more fuel to be removed from system (e.g., injecting less andless fuel) over time, while the ratio remains generally at a desiredratio (e.g., λ=1.0). In other words, in order to maintain the desiredair/fuel ratio, the amount of fuel continues to decrease over time. Whenthis trend is noticed over time, a negative O₂ correction can beindicated. The negative O₂ correction may be analyzed at certain timeincrements (e.g., 30 second increments) to see if the trend of utilizingless fuel is continuing. After a certain length of time of negative O₂correction occurring, it can be inferred that the engine is operating ina confined space in which less and less oxygen is fed into the intake,and therefore more and more fuel must be removed to maintain the desiredair/fuel ratio. The controller can automatically shut down the engineaccordingly.

Speed density equations can take into account temperature and pressureof the air so that the air mass data is compensated for theseenvironmental factors. If the controller notices a negative O₂correction occurring, this infers that the air is “thinner” over time orhas oxygen being consumed from the ambient environment. This indicatesthat the engine is operating in a confined space, and the engine can becommanded to automatically shut down. This may also indicate an increasein altitude, which may be uncommon for a generator in use. Thecontroller can compare barometric pressure if so equipped to rule out anincrease in altitude as the cause of the negative O₂ correction.

Therefore, in one embodiment, the oxygen sensor is a switch type,indicating the presence or absence of oxygen in the exhaust byoutputting a corresponding signal. Based on a presence of oxygen in theexhaust, the controller alters the fuel injection opening or timing suchthat less fuel is provided into the combustion chamber (e.g., tomaintain a specific air/fuel ratio, such as stoichiometric in oneembodiment). In other words, fuel is removed from the air/fuel mixture.This is a negative O₂ correction. Based on a negative O₂ correctionoccurring over time, which causes fuel injection to inject an amount offuel per cycle at a reduced rate over time as explained above, thecontroller commands the engine to automatically shut down based on aninference that the engine is operating in a confined space in whichoxygen is being depleted from the confined space. In an embodiment, thecontroller can command the fuel injector to inject less fuel in responseto the output of the oxygen sensor in order to maintain the air/fuelratio at a desired ratio, and can command the engine to shut down inresponse to the controller continuing to command less and less fuel overtime in order to maintain the air/fuel ratio at the desired ratio.Removing fuel from the air/fuel mixture is typical in order to maintainthe air/fuel ratio at its desired ratio for proper combustion. However,when the fuel is continuing to be removed over time such that less andless fuel is used in combination with the air, negative O₂ correction isoccurring over this time and the controller can automatically shut downthe engine.

As explained, estimation of the size of the enclosure or roomsurrounding the engine may be made with only the oxygen sensor, and notrelying on data from other sensors such as the intake temperaturesensor. For example, in one embodiment (with rounded numbers for ease ofunderstanding), the engine is a 500 cc (0.0005 cubic meter) engine, andthe room volume is 10 cubic meters. For each combustion event of roughly500 cc, all of the O₂ is consumed before being pushed back into theroom. As this occurs over time, the amount of O₂ in the room by volumedecreases as it is exchanged for other chemical compounds (like CO andCO₂). Because the exhaust is recirculating to the intake, the amount ofO₂ in the room is not a simple calculation. However, all O₂ in thecylinder during combustion is consumed. For the first combustion event,it can be assumed that 500 cc (0.0005 cubic meters) worth of air is used(0.005% of the room), and thus roughly 21% of that air is O₂ that isbeing consumed. That same amount of O₂ is being removed from theenclosure. Therefore, the rate of depletion of oxygen directlytranslates to an estimated size of the room. Knowing the rate of changein O₂ due to each combustion event as well as the displacement of theengine allows the controller to estimate the room size of 10 cubicmeters.

While the use of timers is explained herein, it should be understoodthat such use is only in certain embodiments. In various embodiments, anestimation of the size of the room as described herein is not related tosetting a timer to shut down; as soon as the controller determines thesize of the room based on the exemplary methods described herein, theengine can be immediately shut down.

FIG. 5 provides another example of an algorithm employed by thecontroller for automatically shutting down the engine. At 502, thecontroller once again determines if the engine is running to initiatethe algorithm. At 504, the oxygen content of the exhaust is againdetermined according to the methods described herein. At 506, thetemperature of the intake is determined according to methods describedherein.

At 508 the controller compares the rate of change of the oxygen content

$( {\frac{{dO}_{2}}{dt}} )$

to a corresponding threshold, similar to the methods explained above.For example, the oxygen sensor may be a switch-type sensor describedabove and the negative O₂ correction described above may be indicatingthe engine is running in a confined space. If negative O₂ correction isseen occurring, this too is contemplated as meaning that the oxygencontent is changing at a rate that exceeds a threshold. If the oxygencontent is changing at a rate that exceeds the threshold, the algorithmproceeds to 510 in which the controller compares the rate of change ofthe temperature

$( {\frac{dT}{dt}} )$

to a corresponding threshold. The threshold may be, for example, 1degree per 100 seconds. Again, this threshold may vary based on thedetermined size of the room.

In this embodiment, both the oxygen content of the exhaust and thetemperature of the intake must be changing at a rate exceedingrespective thresholds in order for the engine to be automatically shutdown at 512. This may provide an increased assurance that the engine isoperating in a confined space than merely looking at one variable alone.

Comparing exhaust oxygen content and intake temperature are not the onlyembodiments contemplated herein. The controller can also compare achange in load on the engine and a change in power output of thegenerator run by the engine. If the load on the engine is increasingwhile a power output by the generator is decreasing or remainingrelatively constant, this may indicate the engine is operating in aconfined space.

FIG. 6 provides another embodiment of such an algorithm 600 to shut downthe engine. At 602, the controller determines that the engine is on. At604, the controller determines the load placed on the engine. This maybe provided by the pressure sensor on the intake (as disclosed in the'793 Patent, for example). A decrease in air pressure entering theintake may indicate an increased load on the engine. The throttleposition sensor may also indicate load, as an increased (e.g., moreopen) position of the throttle plate to allow more air/fuel to enter thecrank case may be necessary to do the increased load on the engine. Adecrease in air mass volume measurement from an associated sensor mayalso indicate an increased load.

At 606, the controller determines the power output of the portablegenerator. This may be provided by a sensor indicating watts, voltage,or amperage produced by the generator. If the power output of thegenerator remains relatively constant while the load placed on theengine (e.g., throttle angle) is steadily increasing over time, this canindicate the engine operating in a confined space. For example,generators (including those with carbureted engines) typically areprogrammed to operate at a constant speed (e.g., 3600 rpm) to output aconstant power. If the generator is operating in a confined space,oxygen is being removed from the environment; the generator mustaccommodate accordingly (e.g., by increasing the throttle angle to allowmore oxygen in) in order to maintain the constant speed. Typical engineswould operate by opening the throttle more and more until the engine cannot produce enough torque to maintain the generator load, causing theengine's rpm to sag and the engine to eventually stall. The inventiveconcepts in this disclosure recognize and monitor the load placed on theengine over time (e.g., the throttle angle over time) and comparing itto the power output or speed of the engine. For example, if thegenerator continues to increase the throttle angle over time while theengine speed or power output continues to remain constant, thecontroller can infer the generator is operating in a confined space; thecontroller can shut down the engine accordingly.

In one particular embodiment, the engine is provided with a flyballgovernor to control the speed of the engine. The governor is connectedto the throttle valve, and is mechanically linked to the engine output.As the speed of the engine increases, the kinetic energy of the flyballsincreases, which allows lever arms to move outwardly against gravity. Ifthe motion of these lever arms moves far enough, the lever arms causethe throttle valve angle to decrease. This fuel entering the combustionchamber thereby decreases, causing the speed of the engine to reduce,thereby preventing over-speeding of the engine. This can be particularlybeneficial in applications such as generators in which a constant enginespeed (and therefore electric power output) is provided. In such anapplication, if the generator continues to increase the throttle angleover time while the engine speed or power output continues to remainconstant as governed by the flyball governor, the controller can inferthe generator is operating in a confined space; the controller can shutdown the engine accordingly.

For example, at 608, the controller compares the absolute value of therate of change of the load placed on the engine

$( {\frac{dLOAD}{dt}} )$

to a respective threshold, and the rate of change of the power outputfrom the generator

$( {\frac{dPOWER}{dt}} )$

to a respective threshold. If the magnitude of the rate of change of theload placed on the engine exceeds its corresponding load threshold(threshold_(LOAD)) and the rate of change of the power exceeds itscorresponding power threshold (threshold_(POWER)), the controller infersthat the engine is operating in a confined space. In short, in oneembodiment, if the throttle is opening more and more to allow more airinto the combustion chamber, and the amount of power is eitherdecreasing or not correlating to an expected power output in response tothe opening of the throttle, the controller can shut down the engine.The controller can also determine the size of the room by utilizing alookup table that provides an estimated volume of the enclosed spacebased on these rates of change. If the engine is indeed operating in theconfined space, the controller shuts down the engine at 610.

In one or more embodiments, and as explained above, the switching of theoxygen sensor (e.g., sensor 248) may be analyzed to determine whether toautomatically shut down the engine. For example, the output of theoxygen sensor (e.g., voltage) may fluctuate between a reading indicatinga rich air/fuel mixture (e.g., high voltage output) and a readingindicating a lean air/fuel mixture (e.g., low voltage output). Thisoscillation may be between 0.15V and 0.85V with a frequency of 1 Hz. Thefrequency may change due to, among other things, the closed-loop systemdescribed above in which fuel is removed from the air/fuel mixture andthe output of the oxygen sensor may be analyzed again for acorresponding change. The removal of fuel causes a change in the oxygensensor output, and the controller again reviews the oxygen sensor outputto pull more fuel from the mixture, if necessary. This process continuesover time to maintain a constant desired air/fuel ratio. If the removalof fuel continues over time while the desired air/fuel ratio remainsconstant, the engine can be commanded by the controller to shut down.

While not illustrated, other embodiments of automatic engine shutdownand determinations of room size are contemplated. For example, thecontroller may compare an increase in throttle angle position (e.g.,opening) to a decrease in engine speed. If the throttle angle positionis opening at a rate exceeding a threshold, and the absolute value ofthe decrease in engine speed is decreasing at a rate exceeding athreshold, the controller can infer the engine is operating in anenclosed space. The intake air temperature can also be added to thisembodiment, such that it also may be necessary that the intake airtemperature is increasing at a rate exceeding a threshold to cause theengine to shut down.

In another embodiment, air temperature alone is evaluated. For example,if the intake temperature is increasing at a rate exceeding a thresholdthat may be dependent on the determined room size, the engine may shutdown. Alternatively or additionally, the controller may be programmed toautomatically shut down the engine when the temperature itself exceeds athreshold (e.g., 140 degrees Celsius) even if the rate is increasingslowly at a rate that does not exceed the threshold. It should be notedthat engine operation in free air is an infinite heat sink. If theintake air determined to be a consistent temperature or even reducingtemperature, this would not be consistent with confined space operationand the engine may not be commanded to shut down.

As explained above, a wideband oxygen content sensor may be provided onthe intake in certain embodiments. The readings of this sensor alone cancause the controller to shut down the engine. For example, if thewideband O₂ sensor indicates that the oxygen content in the intake (andthus the surrounding air) is less than a predetermined value such as 21%oxygen, then the controller can assume the engine is being operated in aconfined space and can automatically shut down the engine. Thepredetermined value may be other set limits lower than 21% oxygenaccording to different applications. For instance, some controlstrategies may place the predetermined value at 19% oxygen.

In one or more embodiments explained above, time may also be a factor todetermine when to shut down the engine. For example, if the rate ofchange of a certain value (e.g., oxygen content, temperature, etc.) isexceeding its threshold, the engine will not shut down unless the rateof change is exceeding the threshold for a certain time. In other words,a time delay or hysteresis may be provided to the values to preventshutdowns at improper times when the engine may, in fact, not beoperating in an enclosed space. Said another way, once it is determinedthat the engine is running in an enclosed space according to any of theembodiments described above, the controller may not shut down the engineuntil it is determined that the engine is running in the confined spacefor a certain time.

While certain embodiments described above may be directed to portablegenerators, it should be understood that the present disclosure is notlimited to portable generators. The teachings of this disclosure can beimplemented into various structures with small (e.g., two-stroke)engines. The teachings of this disclosure can also be implemented intofour-stroke engines.

In certain embodiments, it may be useful to use as little number ofsensors as possible for shutting off the engine. In direct injectionengines, there may be many sensors that provide a variety of data.However, in carburetor engines or small two-stroke engines, the sameamount of data capabilities may not be possible. Therefore, according tosome embodiments, the controller may be programmed to shut down theengine based on a determination that the engine is in a confined spaceindicated by the temperature and/or the oxygen content alone, withoutother information being necessary for such a procedure. For example, inone embodiment, the controller is programmed to estimate the size of theroom and shut down the engine based on the oxygen sensor alone. Inanother embodiment, the controller is programmed to estimate the size ofthe room and shut down the engine based on the temperature sensor alone.

As explained above, the determination of the room size may be utilizedin combination with other algorithms explained above during an automaticengine shutdown procedure. The determined room size may determine thesensitivity of the system. For example, a determination of a relativelysmall room size may require the system to react more quickly afterstartup (e.g., reducing the amount of the time delay until the data isrelied upon for shutting down the engine) or increase the frequency ofperiodic sampling of engine operation data. As the determined size ofthe room increases, the reaction of the system and frequency of periodsampling can reduce or relax.

Typical fuel systems clog or degrade with age, which requires a need forpositive O₂ correction, or the addition of fuel to maintain stoic. Toquite the contrary, the control system of this disclosure can usenegative O₂ correction, or a removal of fuel, to maintain stoic.Negative O₂ correction has been explained above, in which the controllercontrols the air/fuel mixture just slightly rich/lean of stoic andaltering the mixture based on switching of a switch-based oxygen sensoron the exhaust. Negative O₂ correction requires a lowering of fuel sentto the combustion chamber in order to maintain a stoic combustion.

The processes, methods, or algorithms disclosed herein can bedeliverable to/implemented by a processing device, controller, orcomputer, which can include any existing programmable electronic controlunit or dedicated electronic control unit. Similarly, the processes,methods, or algorithms can be stored as data and instructions executableby a controller or computer in many forms including, but not limited to,information permanently stored on non-writable storage media such as ROMdevices and information alterably stored on writeable storage media suchas floppy disks, magnetic tapes, CDs, RAM devices, and other magneticand optical media. The processes, methods, or algorithms can also beimplemented in a software executable object. Alternatively, theprocesses, methods, or algorithms can be embodied in whole or in partusing suitable hardware components, such as Application SpecificIntegrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs),state machines, controllers or other hardware components or devices, ora combination of hardware, software and firmware components.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments of the invention that may not beexplicitly described or illustrated. While various embodiments couldhave been described as providing advantages or being preferred overother embodiments or prior art implementations with respect to one ormore desired characteristics, those of ordinary skill in the artrecognize that one or more features or characteristics can becompromised to achieve desired overall system attributes, which dependon the specific application and implementation. These attributes caninclude, but are not limited to cost, strength, durability, life cyclecost, marketability, appearance, packaging, size, serviceability,weight, manufacturability, ease of assembly, etc. As such, to the extentany embodiments are described as less desirable than other embodimentsor prior art implementations with respect to one or morecharacteristics, these embodiments are not outside the scope of thedisclosure and can be desirable for particular applications.

What is claimed is:
 1. A portable generator comprising: an engineconfigured to power an electric energy source, the engine having anintake passage configured to transfer an intake, a combustion chamber,and an exhaust passage selectively coupled to the combustion chamber andconfigured to transfer an exhaust after combustion within the combustionchamber; an oxygen sensor configured to output a signal indicating anoxygen content; and a controller coupled to the oxygen sensor andprogrammed to shut down the engine based on the signal over time.
 2. Theportable generator of claim 1, wherein the oxygen sensor is disposed inor adjacent to the exhaust passage such that the signal indicates oxygencontent of the exhaust.
 3. The portable generator of claim 2, whereinthe oxygen sensor is a switch-type sensor configured to detect apresence or absence of oxygen in the exhaust.
 4. The portable generatorof claim 3, wherein the engine further includes a fuel injector forinjecting fuel directly or indirectly into the combustion chamber, andwherein the controller is programmed to command the fuel injector toinject an amount of fuel based on the signal output by the oxygensensor.
 5. The portable generator of claim 4, wherein the controller isprogrammed to shut down the engine in response to the amount of fuelbeing injected decreasing over time.
 6. The portable generator of claim5, further comprising one or more additional sensors configured tooutput signals to the controller, wherein the controller is programmedto determine an air-to-fuel ratio based on the signals from the one ormore additional sensors, and wherein the controller is programmed toshut down the engine in response to the amount of fuel being injecteddecreasing over time while the air-to-fuel ratio is maintained at adesired ratio.
 7. The portable generator of claim 1, wherein the oxygensensor is disposed in or adjacent to the intake passage such that thesignal indicates oxygen content of an atmosphere about the generator. 8.The portable generator of claim 7, wherein the oxygen sensor is awideband oxygen sensor, and the controller is programmed to shut downthe engine in response to the oxygen sensor indicating a decreasedamount of oxygen in the atmosphere over time.
 9. The portable generatorof claim 1, wherein the generator does not include a carbon monoxidesensor configured to detect an amount of carbon monoxide in the exhaust.10. A system for automatically shutting down an engine of a portabledevice, the system comprising: an internal combustion engine; apower-generating unit coupled to the engine and configured to generateelectric power from rotation of the engine; a first sensor configured tooutput a first signal indicating an amount of power output from thepower-generating unit; a second sensor configured to output a secondsignal indicating a load placed on the engine; and a controllerprogrammed to compare the first signal to the second signal, and shutdown the engine in response to the load placed on the engine increasingover time while the rotational speed of the engine remains relativelyconstant.
 11. The system of claim 10, wherein the first sensor is anengine-speed sensor and the first signal indicates a rotational speed ofthe engine which correlates to the power output from thepower-generating unit, such that the controller is programmed to shutdown the engine in response to the load placed on the engine increasingover time while the power output from the power-generating unit remainsrelatively constant.
 12. The system of claim 10, wherein the firstsignal indicates at least one of a watts, voltage, or amperage output bythe power-generating unit.
 13. The system of claim 10, wherein theengine includes a throttle plate configured to alter an amount of airinto a combustion chamber of the engine.
 14. The system of claim 13,wherein the second sensor is a throttle position sensor and the secondsignal indicates a position of the throttle plate such that thecontroller is programmed to shut down the engine in response to theposition of the throttle plate increasing over time while the rotationalspeed of the engine remains relatively constant.
 15. The system of claim13, wherein the second sensor is an air pressure sensor located on oradjacent an intake of the engine, and the second signal indicates apressure of an air intake.
 16. The system of claim 10, wherein thecontroller is programmed to command the shutdown of the engine onlyafter an initial delay after the engine has started.
 17. The system ofclaim 10, wherein the system does not include a carbon monoxide sensordisposed in or adjacent to an exhaust passage of the engine.